Adjusting The Carburetor - Stihl MS 240 Instruction Manual

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Adjusting the Carburetor

General Information
The carburetor comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
Changing the setting of the high speed
screw alters the engine's power output
and the maximum off-load engine
speed.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
Standard Setting
N
Shut off the engine
N Check the air filter and clean or
replace if necessary.
N Check the spark arresting screen
(country-specific) in the muffler and
clean or replace if necessary.
30
H L
3/4 1
N Turn high speed screw (H)
counterclockwise as far as stop (no
more than 3/4 turn).
N Turn the low speed screw (L)
carefully clockwise as far as stop,
then turn it back 1 turn.
Adjusting Idle Speed
Engine stops while idling
N
Carry out standard setting on low
speed screw (L).
N Turn the idle speed screw (LA)
clockwise until the chain begins to
run – then back it off 1/4 turn.
Chain runs when engine is idling
N Carry out standard setting on low
speed screw (L).
N Turn the idle speed screw (LA)
counterclockwise until the chain
stops moving – then turn it another
1/4 turn in the same direction.
If the chain continues moving
when the engine is idling, have
your saw checked and repaired by
your servicing dealer.
Erratic idling behavior, poor
acceleration (even though standard
setting of low speed screw is correct)
N Idle setting is too lean: Turn the low
speed screw (L) counterclockwise
until the engine runs and
accelerates smoothly.
It is usually necessary to change the
setting of the idle speed screw (LA) after
every correction to the low speed
screw (L).
Fine tuning for operation at high
altitude or at sea level
A slight correction of the setting may be
necessary if engine does not run
satisfactorily:
N Check the standard setting.
N Warm up the engine.
N Turn high speed screw (H) slightly
clockwise (leaner) – no further than
stop.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
MS 240